The catalytically active form of toluene-4-monooxygenase is derived from the tmoA-f gene cluster from Pseudomonas mendocina KR1. Prelimanry kinetic results suggest that the tmoD gene product (11.6 kDa) possess some ability to regulate catalytic activity. We are undertaking a preliminary 1H characterization of this regulatory subunit in order to determine the feasibility of determining its structure of by NMR.